* Make document write requests immutable
Previously, write requests were mutated at the
transport level to update request version, version type
and sequence no before replication.
Now that all write requests go through the shard bulk
transport action, we can use the primary response stored
in item level bulk requests to pass the updated version,
seqence no. to replicas.
* incorporate feedback
* minor cleanup
* Add bwc test to ensure correct index version propagates to replica
* Fix bwc for propagating write operation versions
* Add assertion on replica request version type
* fix tests using internal version type for replica op
* Fix assertions to assert version type in replica and recovery
* add bwc tests for version checks in concurrent indexing
* incorporate feedback
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